Star light, star bright: The transit method for detecting planets beyond our solar system works by looking for the drop in brightness of a star that’s caused by a planet passing in front of it. Astronomers use the data to calculate the size of the planet and its distance from its star.
The transit method employed by the CoRot satellite uses a telescope to collect light that is then fed to a two-part camera. One part of the camera is designed to look for stars; the other is optimized to detect the subtle variation in a star’s light. European researchers built a device to shield the camera from light coming from sources other than those objects at which the telescope is looking.
NASA’s Kepler satellite, which launched last year, is also using the transit method to look for Earthlike planets. Wright says the spacecraft will “revolutionize our search for habitable planets.” Kepler has 42 detectors that can measure the brightness of 150,000 stars and stores the data every six seconds. “No one has ever built a [space-based] instrument with this kind of precision,” says William Borucki, science principal investigator for the Kepler mission.
John Johnson, an assistant professor of astronomy at Caltech, says the new finding by CoRot foreshadows the work that astronomers expect Kepler to make over the next few years. Johnson predicts that Kepler will find the first inhabitable “Earth” outside our solar system in the next three to six years.
For astronomers to really understand the composition of exoplanets they discover, they will need to use an emerging method called direct detection. This technology uses an adaptive optics system and a device called a coronagraph, which blocks out as much light from the star as possible, to image the planet. The Hubble Space Telescope was able to image a planet around the star named Fomalhuat using a coronagraph, and only two other telescopes have this capability, the Keck Observatory in Hawaii and the Very Large Telescope in Chile.
Direct imaging instruments are being built for the Gemini observatory in Chile, the Subaru telescope in Japan, and the Very Large Telescope. NASA’s next space telescope, the James Webb Space Telescope, set to launch in 2013, will also use direct detection. As part of a Technology Development program, NASA recently issued a two-year $784,000 grant to researchers at Rochester Institute of Technology in New York and MIT Lincoln Laboratory, to modify one of Lincoln Lab’s photon detectors for imaging planets. The detector counts individual photons digitally, says Brian Aull, a technical staff member at MIT Lincoln Laboratory. “The advantage is that it is able to detect very faint objects with better signal-to-noise characteristics than conventional detector technology.”
“The main thing is finding planets, because in order to better understand our solar system, we have to understand how other planetary systems formed,” says Borucki. If astronomers can find lots of Earthlike planets, the next step is to develop instruments that can look for signatures of life. “We need to know: is there life out there, or are we alone?”